Something occurred to me, after discussing break in periods with some friends of mine, not related to the G8, but it brought me back to thinking about my new car.

From my understanding, the typical reasoning behind the break in, is to ensure that the rings have "seated" correctly. Also from my understanding, AFM turns off the valvetrain, spark, and fuel on up to 4 of the cylinders.

So, here is the question. How does GM assume that all 8 rings will seat properly, in unison, if the car is constantly turning off cylinders. Is AFM disabled for a certain set period of time, to ensure this process goes off without a hitch. Could be possibly see higher mpg after XXXX miles?

Maybe my understanding of how AFM works or how break in is supposed to work, is flawed. I'm an engineer, so I spend a lot of time thinking about how systems work.

Does anyone have any insight or speculation about this? I know with modern machining processes, break in is almost a thing of the past, but even still. It has to have some sort of impact and GM must have thought about this during the engineering of the motor.

You motor should be broken in from the factory.

Mostly what manufacturer break in is for now is the rest of the drivetrain.

But AFM shouldn't cause any trouble in break in anyway as it doesn't come on unless you're cruising. You shouldn't be doing much cruising during break in. :)

But AFM shouldn't cause any trouble in break in anyway as it doesn't come on unless you're cruising. You shouldn't be doing much cruising during break in. :)

From my understanding, even "in town", the car likes to work off 6 cylinders, which I wouldn't tag as "cruising". I'm not so much worried about the break in procedure, it was more of a technical question, of whether or not GM had AFM working differently under a certain amount of miles or not.

From my understanding, even "in town", the car likes to work off 6 cylinders, which I wouldn't tag as "cruising". I'm not so much worried about the break in procedure, it was more of a technical question, of whether or not GM had AFM working differently under a certain amount of miles or not.

From what I've read, AFM is either ACTIVE (4 cylinders) or INACTIVE (8 cylinders). It's doesn't do any progressive deactivating, 8 to 6 to 4 cylinders.

It's either 4, or 8 cylinders. No 6 cylinder operational mode on the motor.

Basically, it activates in any light load application at certain speeds I think.

Regardless, what GM recommends in the manual should be taken as de-facto advice on how to break in the car. They wouldn't put it in there if they thought it would hurt the car.

If you are worried about it you can drive in manual through the entire "break in" period and it won't activate AFM.

If you are worried about it you can drive in manual through the entire "break in" period and it won't activate AFM.

You're all misunderstanding me. I was just curious if there was some technical means around this, from GM, for the first, say, 1000 miles. It doesn't concern me at all. Modern engines don't really need to be broken in like they used to.

If you are worried about it you can drive in manual through the entire "break in" period and it won't activate AFM.

First I recall seeing this -
and I have read a lot about AFM & DoD.
Source???
Thanks,
- Ray
Very curious...

Source???

Personal experience... Driving in manual with engineering mode on, in 6th gear at steady speed the AFM has never kicked in.

Personal experience... Driving in manual with engineering mode on, in 6th gear at steady speed the AFM has never kicked in.

Fascinating.
Thanks!
And good to know - as I am in the habit of ** ALWAYS ** driving
Every car I have had with the ‘manumatic’ feature ( including my current Corvette, w/6L80 & 6.0L V8, but NO AFM ) in manual mode.

I wonder why the AFM is disabled in that mode????

- Ray
Even more curious now . . .

I wonder why the AFM is disabled in that mode????


To remove the delay to switching back to all 8 cylinders maybe? Its meant for performance, so why bother switching AFM on?

To remove the delay to switching back to all 8 cylinders maybe? Its meant for performance, so why bother switching AFM on?

The AFM engagement is described ( typically ) as “seamless”.
And ( according to GM’s documentation ): “The transition takes less than 20 milliseconds, and can’t be detected by the driver.”

Does not seem logical or reasonable – to me.
And I keep mine in Manual Mode partly to preclude ‘automatic’ downshifts, based on my speed & throttle position changes.
I ( very strongly ) prefer to time my own downshifts & upshifts.
- Ray
Appreciate the information – not pleased with GM’s choice here. . .

Something occurred to me, after discussing break in periods with some friends of mine, not related to the G8, but it brought me back to thinking about my new car.

From my understanding, the typical reasoning behind the break in, is to ensure that the rings have "seated" correctly. Also from my understanding, AFM turns off the valvetrain, spark, and fuel on up to 4 of the cylinders.

So, here is the question. How does GM assume that all 8 rings will seat properly, in unison, if the car is constantly turning off cylinders. Is AFM disabled for a certain set period of time, to ensure this process goes off without a hitch. Could be possibly see higher mpg after XXXX miles?

Maybe my understanding of how AFM works or how break in is supposed to work, is flawed. I'm an engineer, so I spend a lot of time thinking about how systems work.

Does anyone have any insight or speculation about this? I know with modern machining processes, break in is almost a thing of the past, but even still. It has to have some sort of impact and GM must have thought about this during the engineering of the motor.

You're all misunderstanding me. I was just curious if there was some technical means around this, from GM, for the first, say, 1000 miles. It doesn't concern me at all. Modern engines don't really need to be broken in like they used to.


I don't think anyone is misunderstanding you.
Your initial question, in bold type above, was answered in the first post. The engines are broken in at the factory before going in the vehicle. During a bench break in, I wouldn't think that AFM would even come into play.

mac

The AFM engagement is described ( typically ) as “seamless”.
And ( according to GM’s documentation ): “The transition takes less than 20 milliseconds, and can’t be detected by the driver.”

Does not seem logical or reasonable – to me.
And I keep mine in Manual Mode partly to preclude ‘automatic’ downshifts, based on my speed & throttle position changes.
I ( very strongly ) prefer to time my own downshifts & upshifts.
- Ray
Appreciate the information – not pleased with GM’s choice here. . .

I can tell when it comes on.... it was so obvious after I changed the rear mufflers out. Breaking n the motor occurs when you're punching it up and down revs and through the gears... the afm only kicks in when you are bearly touching the gas pedal. So anytime you are not touching the gas the afm kicks in but as soon as you hit it that helps with the break in and the afm switches off real quick.

Basically you have nothing to worry about. It only really helps when you're on the freeway or long open road.

I don't think anyone is misunderstanding you.
Your initial question, in bold type above, was answered in the first post. The engines are broken in at the factory before going in the vehicle. During a bench break in, I wouldn't think that AFM would even come into play.

mac

I've heard different statements abut the break in at the factory. I have one source (engineer for GM) that states that every XXX motor is taken off the line, and run through a YYY hour quality control dyno run.

From non-GM people, I've heard that every motor is broken in at the factory. Coming from a business that has strict QA guidelines (military level), the cost of doing such a thing would be cost prohibitive, for a $30,000 car.

I'm not calling anyone a liar, I just haven't heard any official word from GM on the factory break-in.

And my reference to the "misunderstanding", was more to the effect of... I'm not worried, I'm more curious about how the system works. Pure curiosity...

Something occurred to me, after discussing break in periods with some friends of mine, not related to the G8, but it brought me back to thinking about my new car.

From my understanding, the typical reasoning behind the break in, is to ensure that the rings have "seated" correctly. Also from my understanding, AFM turns off the valvetrain, spark, and fuel on up to 4 of the cylinders.

So, here is the question. How does GM assume that all 8 rings will seat properly, in unison, if the car is constantly turning off cylinders. Is AFM disabled for a certain set period of time, to ensure this process goes off without a hitch. Could be possibly see higher mpg after XXXX miles?

Maybe my understanding of how AFM works or how break in is supposed to work, is flawed. I'm an engineer, so I spend a lot of time thinking about how systems work.

Does anyone have any insight or speculation about this? I know with modern machining processes, break in is almost a thing of the past, but even still. It has to have some sort of impact and GM must have thought about this during the engineering of the motor.

Why would AFM affect break-in of cylinder bores/piston rings? The pistons are stilling moving up and down in the cylinders, regardless of AFM.

From the edmunds article on the holden plant, every G8 and Commodore undergoes a dyno run at the factory.

Why would AFM affect break-in of cylinder bores/piston rings? The pistons are stilling moving up and down in the cylinders, regardless of AFM.

Because heat causes the rings to "seat". If the cylinder isn't firing, it has a different "heat profile" then the other cylinders.

From the edmunds article on the holden plant, every G8 and Commodore undergoes a dyno run at the factory.

Thanks for the info. Its what I was looking for.

Because heat causes the rings to "seat". If the cylinder isn't firing, it has a different "heat profile" then the other cylinders.

Good point, and this may be why GM recommends against long periods of steady-speed driving during the first 600 miles.

Because heat causes the rings to "seat". If the cylinder isn't firing, it has a different "heat profile" then the other cylinders.

But minimally different. The water jacket temp doesn't vary. And from what I've read about most AFM's the spark plugs never shut off, as it helps scavenge any unburnt fuel remaining in the cylinders.

Good point, and this may be why GM recommends against long periods of steady-speed driving during the first 600 miles.So does every car maker....

This is an interesting question, just how does the deactivation effect wear-n-tear? I’m also just curious, no doubt the engineers have sorted the details out. I’m just interested in the details of how the engine is designed to make the magic work reliably. Are the same cylinders always deactivated? The heat cycles on different piston/sleeves would seemingly cause different wear characteristics over the short haul (break-in) and long haul (longevity of the engine). The water jacket only dissipates the heat generated in the combustion chamber, so an active-vs-deactivated cylinder would have a substantially different internal temperature. There must be some engineering tricks used to make it reliable. Wikipedia has some interesting info but no details about the design.

I broke my G8 GT in at 150miles. Several WOT runs and lots of manual and sport mode driving. Do not be afraid to hammer your car before 600miles! A couple of things I noticed right away, Tranny shifts smoothly in drive and the shifts are pretty crisp in Sport mode in Manual mode.

I did the same with my 6 speed 04 GTO and that car ran flawlessly for 76000miles and I was able to run a 13.3@104 with it, factory stock.

This is an interesting question, just how does the deactivation effect wear-n-tear? I’m also just curious, no doubt the engineers have sorted the details out. I’m just interested in the details of how the engine is designed to make the magic work reliably. Are the same cylinders always deactivated? The heat cycles on different piston/sleeves would seemingly cause different wear characteristics over the short haul (break-in) and long haul (longevity of the engine). The water jacket only dissipates the heat generated in the combustion chamber, so an active-vs-deactivated cylinder would have a substantially different internal temperature. There must be some engineering tricks used to make it reliable. Wikipedia has some interesting info but no details about the design.

Back on topic - this article \ doc includes some details
I don't recall seeing elsewhere...

http://www.fastfieros.com/tech/DOD5_3.htm

My understanding is that AFM = DoD - just a rename.

- Ray
Acronym challenged.........